Suppose, unfortunately, your mathematics and economics professor have decided to give tests 2 days from now and you can only spend a total of 12 hours studying for both exams. After some thought, you conclude that dividing your study time equally between each subject will give you and expected grade of C in each course. For each additional 3 hours study time for one of the subjects, you grade will increase one letter for that subject, and your grade will fall one letter for the other subject.